import pandas as pd

df1 = pd.DataFrame(
    [{"r1": 'a', "r2": 1.2},
     {"r1": "b", "r2": 2.3},
     {"r1": "c", "r2": 2.6},
     {"r1": "d", "r2": 3.0}
     ]
)

print(df1)
df1.set_index("r1", inplace=True)

d1 = {"a":"aa", "b":"bb"}

for k, v in d1.items():
    df1.at[k, "r3"] = v
print(df1)

dd = df1.to_dict(orient="records")
print(dd)

dd2 = df1.to_dict(orient="index")
print(dd2)

d1 = {"r1": 'a', "r2": 1.2}
df = pd.DataFrame.from_dict(d1, orient="index")
print(df)